I have this user price input that I want to allow 0, 1 or 2 decimal digits.

• I'm using ma for decimals.
• I'm not using nor allowing thousand separators.

QUESTION:

I want to replace the input if the user enters a third decimal digit.

Somethin like:

• 5 this is ok
• 5, this is ok, because it's waiting for the decimals
• 5,5 this is ok
• 5,55 this is ok
• 5,555 this is NOT OK, and I want to delete the last digit and go back to 5,55
• 5,555555555555 this is also NOT OK, the user might paste something with extra decimal digits and I want to trim them down to 2 decimals maximum, going back again to 5,55

How can I do this?

I know how I can match the end of the string: /[,\d+]$/

But how can I replace with the first two digits after the ma?

I have this user price input that I want to allow 0, 1 or 2 decimal digits.

• I'm using ma for decimals.
• I'm not using nor allowing thousand separators.

QUESTION:

I want to replace the input if the user enters a third decimal digit.

Somethin like:

• 5 this is ok
• 5, this is ok, because it's waiting for the decimals
• 5,5 this is ok
• 5,55 this is ok
• 5,555 this is NOT OK, and I want to delete the last digit and go back to 5,55
• 5,555555555555 this is also NOT OK, the user might paste something with extra decimal digits and I want to trim them down to 2 decimals maximum, going back again to 5,55

How can I do this?

I know how I can match the end of the string: /[,\d+]$/

But how can I replace with the first two digits after the ma?

• javascript
• regex
• replace
• regex-lookarounds
• regex-group

2 Answers 2

Your pattern [,\d+]$ will match a ma a digit or a plus sign and assert the end of the string.

You could capture in a group 1+ digits, an optional ma and 0-2 digits. then match 0+ digits afterwards and replace with group 1.

^(\d+,?\d{0,2})\d*$

Explanation

• ^ Start of strig
• ( Capture group 1
  • \d+ 1+ digits
  • ,? optional ma
  • \d{0,2} 0 - 2 digits
• ) Close group
• \d* Match 0+ digits
• $ Assert end of string

Regex demo

If you want to keep the part before the decimal, you could use a capturing group^(\d+),?\d{0,2}$ and replace with the first capturing group:

[
  "5",
  "5",
  "5,0",
  "5,00",
  "5,000"
].forEach(s => console.log(s.replace(/^(\d+,?\d{0,2})\d*$/, "$1")));

You could always temporarily convert the ma to a period, parse the float and fix it to 2 decimals, then replace the period with a ma again like below;

let str = '1,567895'; // price value

let val = parseFloat(str.replace(',', '.')).toFixed(2).replace('.', ',');
console.log(val);